We study the pair production, string breaking, and hadronization of a receding electron-positron pair using the bosonized version of the massive Schwinger model in quantum electrodynamics in $1+1$ space-time dimensions. Specifically, we study the dynamics of the electric field in Bjorken coordinates by splitting it into a coherent field and its Gaussian fluctuations. We find that the electric field shows damped oscillations, reflecting pair production. Interestingly, the computation of the asymptotic total particle density per rapidity interval for large masses can be fitted using a Boltzmann factor, where the temperature can be related to the hadronization temperature in QCD. Lastly, we discuss the possibility of an analog quantum simulation of the massive Schwinger model using ultracold atoms, explicitly matching the potential of the Schwinger model to the effective potential for the relative phase of two linearly coupled Bose-Einstein condensates.

We investigate the causality and stability of three different relativistic dissipative fluid-dynamical formulations emerging from a system of classical, ultrarelativistic scalar particles self-interacting via a quartic potential. For this particular interaction, all transport coefficients of Navier-Stokes, Bemfica-Disconzi-Noronha-Kovtun (BDNK), and second-order transient theories can be computed in analytical form. We first show that Navier-Stokes theory is acausal and unstable regardless of the matching conditions. On the other hand, the BDNK theory can be linearly causal and stable for a particular set of matching choices that does not contain the so-called exotic Eckart prescription. In particular, using the Liénard-Chipart criterion, we obtain a set of sufficient conditions that guarantee the stability of the theory. Last, second-order transient hydrodynamic theory in Landau matching is shown to be linearly causal and stable.

We study a lepton-flavored dark matter model and its signatures at a future muon collider. We focus on the less-explored regime of feeble dark matter interactions, which suppresses the dangerous lepton-flavor-violating processes, gives rise to dark matter freeze-in production, and leads to long-lived particle signatures at colliders. We find that the interplay of dark matter freeze-in and its mediator freeze-out gives rise to an upper bound of around TeV scales on the dark matter mass. The signatures of this model depend on the lifetime of the mediator and can range from generic prompt decays to more exotic long-lived particle signals. In the prompt region, we calculate the signal yield, study useful kinematics cuts, and report tolerable systematics that would allow for a $5\sigma$ discovery. In the long-lived region, we calculate the number of charged tracks and displaced lepton signals of our model in different parts of the detector and uncover kinematic features that can be used for background rejection. We show that, unlike in hadron colliders, multiple production channels contribute significantly, which leads to sharply distinct kinematics for electroweakly charged long-lived particle signals. Ultimately, the collider signatures of this lepton-flavored dark matter model are common among models of electroweak-charged new physics, rendering this model a useful and broadly applicable benchmark model for future muon collider studies that can help inform work on detector design and studies of systematics.

We consider multileg ladders of Rydberg atoms which have been proposed as quantum simulators for the compact Abelian Higgs model (CAHM) in $1+1$ dimensions [Y. Meurice, Phys. Rev. D 104, 094513 (2021)] and modified versions of theses simulators such as triangular prisms. Starting with the physical Hamiltonian for the analog simulator, we construct translation-invariant effective Hamiltonians by integrating over the simulator high-energy states produced by the blockade mechanism when some of the atoms are sufficiently close to each other. Remarkably, for all the simulators considered, the effective Hamiltonians have the three types of terms present for the CAHM (electric field, matter charge, and current energy), but in addition, they have terms quartic in the electric field. For the two-leg ladder, these additional terms cannot be removed by fine-tuning the adjustable parameters of currently available devices. For positive detuning, the new terms create highly degenerate vacua, resulting in a very interesting phase diagram. Using numerical methods, we demonstrate the close correspondence between the physical simulator and the effective description for the ground-state energy and real-time evolution. We discuss the phase diagram at fixed geometry with variable Rabi frequency and detuning, and we show that a rich variety of phases can be reached with potential interest in the context of QCD at finite density. We illustrate how the effective description can be used to design simulators with desirable properties from the point of view of constructing hybrid event generators.

Using the entire BABAR $\mathrm{\Upsilon }(4S)$ dataset, the first two-dimensional unbinned angular analysis of the semileptonic decay $\overline{B}\to D{\ell }^{-}{\overline{\nu }}_{\ell }$ is performed, employing hadronic reconstruction of the tag-side $B$ meson from $\mathrm{\Upsilon }(4S)\to B\overline{B}$. Here, $\ell$ denotes the light charged leptons $e$ and $\mu$. A novel data-driven signal-background separation procedure with minimal dependence on simulation is developed. This procedure preserves all multidimensional correlations present in the data. The expected ${\sin }^2{\theta }_{\ell }$ dependence of the differential decay rate in the Standard Model is demonstrated, where ${\theta }_{\ell }$ is the lepton helicity angle. Including input from the latest lattice QCD calculations and previously available experimental data, the underlying form factors are extracted using both model-independent (BGL) and dependent (CLN) methods. Comparisons with lattice calculations show flavor SU(3) symmetry to be a good approximation in the $B_{(s)}\to D_{(s)}$ sector. Using the BGL results, the CKM matrix element $|V_{cb}|=(41.09\pm 1.16)\times {10}^{-3}$ and the Standard Model prediction of the lepton-flavor universality violation variable $\mathcal{R}(D)=0.300\pm 0.004$, are extracted. The value of $|V_{cb}|$ from $\overline{B}\to D{\ell }^{-}{\overline{\nu }}_{\ell }$ tends to be higher than that extracted using $\overline{B}\to D^{*}{\ell }^{-}{\overline{\nu }}_{\ell }$. The Standard Model $\mathcal{R}(D)$ calculation is at a $1.97\sigma$ tension with the latest HFLAV experimental average.

Carroll black holes with an associated Carroll temperature were introduced recently. So far, it is unclear if they exhibit a Hawking-like effect. To solve this, we study scalar fields on Carroll black hole backgrounds. Inspired by anomaly methods, we derive a Hawking-like energy-momentum tensor compatible with the Carroll temperature and the Stefan-Boltzmann law. Key steps in our derivation are the finiteness of energy at the Carroll extremal surface and compatibility with the Carroll-Ward identities, thereby eliminating, respectively, the Carroll analogs of the Boulware and Unruh vacua.

Gauging isometries of four-dimensional $\mathcal{N}=2$ supergravity theories yields an $\mathcal{N}=2$ supersymmetric theory with a scalar potential. In this paper, we study the well-known constraints for four-dimensional $\mathcal{N}=2$ Minkowski vacua of such theories. We propose that classically a projective special Kähler submanifold of the projective Kähler target space of the ungauged theory describes the moduli space of the complex scalar fields of massless vector multiplets for $\mathcal{N}=2$ Minkowski vacua configurations, which then receives quantum corrections from integrating out massive fields. Subloci of projective special Kähler manifolds appear as supersymmetric flux vacua in the context of type IIB Calabi–Yau threefold compactifications with background fluxes as well. While these flux vacua equations arise from the critical locus of an $\mathcal{N}=1$ superpotential, we show that these equations can also be obtained from the $\mathcal{N}=2$ supersymmetric Minkowski vacuum equations of gauged $\mathcal{N}=2$ supergravity theories upon gauging suitable isometries in the semiclassical universal hypermultiplet sector of type IIB string Calabi–Yau threefold compactifications. Thus, we give an intrinsic $\mathcal{N}=2$ supersymmetric interpretation to the flux vacua equations.

We study the classical Liouville field theory on Riemann surfaces of genus $g>1$ in the presence of vertex operators associated with branch points of orders $m_i>1$. In order to do so, we will consider the generalized Schottky space ${\mathfrak{S}}_{g,n}(\mathit{m})$ obtained as a holomorphic fibration over the Schottky space ${\mathfrak{S}}_g$ of the (compactified) underlying Riemann surface. The fibers of ${\mathfrak{S}}_{g,n}(\mathit{m})\to {\mathfrak{S}}_g$ correspond to configuration spaces of $n$ orbifold points of orders $\mathit{m}=(m_1,\dots ,m_n)$. Drawing on the previous work of Park et al. [Adv. Math. 305, 856 (2017)] as well as Takhtajan and Zograf [Lett. Math. Phys. 109, 1119 (2018); L. A. Takhtajan and P. ZografLett. Math. Phys.114, 60 (2024)], we define Hermitian metrics ${\mathsf{h}}_i$ for tautological line bundles ${ℒ}_i$ over ${\mathfrak{S}}_{g,n}(\mathit{m})$. These metrics are expressed in terms of the first coefficient of the expansion of covering map $J$ near each singular point on the Schottky domain. Additionally, we define the regularized classical Liouville action $S_{\mathit{m}}$ using Schottky global coordinates on Riemann orbisurfaces with genus $g>1$. We demonstrate that $\exp [S_{\mathit{m}}/\pi ]$ serves as a Hermitian metric in the holomorphic $\mathbb{Q}$-line bundle $ℒ={\otimes }_{i=1}^n{ℒ}_i^{\otimes (1-1/m_i^2)}$ over ${\mathfrak{S}}_{g,n}(\mathit{m})$. Furthermore, we explicitly compute the first and second variations of the smooth real-valued function ${𝒮}_{\mathit{m}}=S_{\mathit{m}}-\pi {\sum }_{i=1}^n(m_i-\frac{1}{m_i})\log {\mathsf{h}}_i$ on the Schottky deformation space ${\mathfrak{S}}_{g,n}(\mathit{m})$. We establish two key results: (i) ${𝒮}_{\mathit{m}}$ generates a combination of accessory and auxiliary parameters, and (ii) $-{𝒮}_{\mathit{m}}$ acts as a Kähler potential for a specific combination of Weil-Petersson and Takhtajan-Zograf metrics that appear in the local index theorem for orbifold Riemann surfaces [Takhtajan and Zograf, Lett. Math. Phys. 109, 1119 (2018)]. The obtained results can then be interpreted in terms of the complex geometry of the Hodge line bundle equipped with Quillen’s metric over the moduli space ${\mathfrak{M}}_{g,n}(\mathit{m})$ of Riemann orbisurfaces and the tree-level approximation of conformal Ward identities associated with quantum Liouville theory.

Understanding the phenomenon of quantum superposition of gravitational fields induced by massive quantum particles is an important starting point for quantum gravity. The purpose of this study is to deepen our understanding of the phenomenon of quantum superposition of gravitational fields. To this end, we consider a trade-off relation of entanglement (monogamy relation) in a tripartite system consisting of two massive particles and a gravitational field that may be entangled with each other. Consequently, if two particles cannot exchange information mutually, they are in a separable state, and the particle and gravitational field are always entangled. Furthermore, even when two particles can send information to each other, there is a trade-off between the two particles and the gravitational field. We also investigate the behavior of the quantum superposition of the gravitational field using quantum discord. We find that quantum discord increases depending on the length scale of the particle superposition. Our results may help understand the relationship between the quantization of the gravitational field and the meaning of the quantum superposition of the gravitational field.

Effective-one-body (EOB) waveforms employed by the LIGO-Virgo-KAGRA Collaboration have primarily been developed by resumming the post-Newtonian expansion of the relativistic two-body problem. Given the recent significant advancements in post-Minkowskian (PM) theory and gravitational self-force formalism, there is considerable interest in creating waveform models that integrate information from various perturbative methods in innovative ways. This becomes particularly crucial when tackling the accuracy challenge posed by upcoming ground-based detectors (such as the Einstein Telescope and Cosmic Explorer) and space-based detectors (such as LISA, TianQin, or Taiji) expected to operate in the next decade. In this context, we present the derivation of the first spinning EOB (SEOB) Hamiltonian that incorporates PM results up to three-loop order: the SEOB-PM model. The model accounts for the complete hyperbolic motion, encompassing nonlocal-in-time tails. To evaluate its accuracy, we compare its predictions for the conservative scattering angle, augmented with dissipative contributions, against numerical-relativity data of nonspinning and spinning equal-mass black holes. We observe very good agreement, comparable, and in some cases slightly better to the recently proposed $w_{\mathrm{EOB}}$-potential model, of which the SEOB-PM model is a resummation around the probe limit. Indeed, in the probe limit, the SEOB-PM Hamiltonian and scattering angles reduce to the one of a test mass in Kerr spacetime. Once complemented with nonlocal-in-time contributions for bound orbits, the SEOB-PM Hamiltonian can be utilized to generate waveform models for spinning black holes on quasicircular orbits.

A viable model for the dense matter equation of state above the nuclear saturation density includes a hadron-to-quark phase transition at densities relevant to compact objects. In this case, stable hybrid hadron-quark stars can arise. An even more interesting scenario is one where the hadron-to-quark phase transition results in the emergence of a third branch of stable compact objects (in addition to white dwarfs and neutron stars). Inherent to the presence of a third family of compact stars is the existence of twin stars—hybrid stars with the same mass as the corresponding neutron stars but with smaller radii. Interestingly, the neutron star–twin star scenario is consistent with GW170817. If twin stars exist in nature, it raises a question about the mechanism that leads to their formation. Here, we explore gravitational collapse as a pathway to the formation of low-mass twin stars. We perform fully general relativistic simulations of the collapse of a stellar iron core, modeled as a cold degenerate gas, to investigate whether the end product is a neutron star or a twin star. Our simulations show that, even with unrealistically large perturbations in the initial conditions, the core bounces well below the hadron-to-quark phase transition density, if the initial total rest mass is in the twin star range. Following cooling, these configurations produce neutron stars. We find that twin stars can potentially form due to mass loss, e.g., through winds, from a slightly more massive hybrid star that was initially produced in the collapse of a more massive core, or if the maximum neutron star mass is below the Chandrasekhar mass limit. The challenge in producing twin stars in gravitational collapse, in conjunction with the fine-tuning required because of their narrow mass range, suggests the rarity of twin stars in nature.

We revisit a class of simple single-field inflation models and demonstrate that they can readily produce a negligible tensor/scalar ratio $r$. Motivated by recent work suggesting the need to introduce higher order operators to stabilize unregulated potentials, as well as by work indicating that such terms can have significant effects on observable predictions, we explicitly construct corrected versions of the quadratic hilltop potential that are motivated by an effective field theory expansion. We employ Markov Chain Monte Carlo methods and optimization techniques to sample viable models and minimize $r$. We find that such potentials can readily lower $r$ values below projected CMB-S4 sensitivity, while still remaining within observable constraints on $n_s$. Furthermore, we find that the minimum $r$ reached for each order of the expansion considered is well described by a power law $r_{\min }(q)\propto q^{-B}$ before asymptoting to a value of $r_{\min }\sim {10}^{-11}$, where $q$ is the order to which the expansion of $V(\varphi )$ is carried out.

In this paper, we propose a novel minimal physical model to elucidate the long-term stochastic variability of blazars. The model is built on the realistic background of magnetized plasma jets dissipating energy through a turbulent cascade process that transfers energy to small-scale structures with highly anisotropic radiation. The model demonstrates the ability to spontaneously generate variability features consistent with observations of blazars under uniformly random fluctuations in the underlying physical parameters. This indicates that the model possesses self-similarity across multiple timescales, providing a natural explanation for the universal power spectral density (PSD) structure observed in different types of blazars. Moreover, the model exhibits that when the cascade process produces a relatively flat blob energy distribution, the spectral index of the model-simulated PSD in the high-frequency regime will be steeper than that predicted by the damped random walk (DRW) model, which is in agreement with recent observations of active galactic nucleus (AGN) variability, providing a plausible theoretical explanation. The model is also able to reproduce the observed fractional variability amplitude (FVA) characteristics of blazars, and suggests that the specific particle acceleration and radiative cooling processes within the blob may not be the key factor shaping the long-term stochastic variability. This minimal model provides a new physical perspective for understanding the long-term stochastic variability of blazars.

We explore an alternative explanation for the low-mass ultracompact star in the supernova remnant HESS J1731-347 using a model-agnostic approach to construct hybrid equations of state. The hadronic part of the hybrid equation of state is constructed using a generalized piecewise polytropic scheme, while the quark phase is described by the generic constant speed of sound model. We assume an abrupt first-order hadron-quark phase transition with a slow conversion speed between phases. Our equations of state align with modern chiral effective field theory calculations near nuclear saturation density and are consistent with perturbative quantum chromodynamics calculations at high densities. Using this theoretical framework, we derive a wide range of hybrid equations of state capable of explaining the light compact object in HESS J1731-347 in a model-independent manner, without fine-tuning. These equations of state are also consistent with modern astronomical constraints from high-mass pulsar timing, NICER observations, and multimessenger astronomy involving gravitational waves. Our results support the hypothesis that the compact object in HESS J1731-347 could plausibly be a slow stable hybrid star.

The spectroscopy of ${\mathrm{\Xi }}^0$ is performed within the relativistic framework of independent quark model. The equal mixture of scalar and vector components in the potential having Martin-like form is considered for the confinement. With the suitable potential parameters for ${\mathrm{\Xi }}^0$, mass spectra for high radial and orbital excitation is calculated. The experimentally observed values of the ground-state magnetic moment, branching ratios, and asymmetry parameters for radiative weak decays, ${\mathrm{\Xi }}^0\to {\mathrm{\Lambda }}^0+{\gamma }^0$ and ${\mathrm{\Xi }}^0\to {\mathrm{\Sigma }}^0+{\gamma }^0$ are obtained to validate the model. The spin parity of experimentally known resonances like $\mathrm{\Xi }(1530)$, $\mathrm{\Xi }(1820)$, and $\mathrm{\Xi }(2030)$ are confirmed through the Regge trajectories in $(J,M^2)$ plane. The spin parity of $\mathrm{\Xi }(1950)$, $\mathrm{\Xi }(2130)$, and $\mathrm{\Xi }(2250)$ are predicted using those Regge trajectories. The radiative decay width and magnetic moment of first resonance is also predicted.

The quantum chromodynamics (QCD) axion may solve the strong $CP$ problem and explain the dark matter (DM) abundance of our Universe. The axion was originally proposed to arise as the pseudo-Nambu-Goldstone boson of global $\mathrm{U}(1{)}_{\mathrm{PQ}}$ Peccei-Quinn (PQ) symmetry breaking, but axions also arise generically in string theory as zero modes of higher-dimensional gauge fields. In this work we show that string theory axions behave fundamentally differently from field theory axions in the early Universe. Field theory axions may form axion strings if the PQ phase transition takes place after inflation. In contrast, we show that string theory axions do not generically form axion strings. In special inflationary paradigms, such as D-brane inflation, string theory axion strings may form; however, their tension is parametrically larger than that of field theory axion strings. We then show that such QCD axion strings overproduce the DM abundance for all allowed QCD axion masses and are thus ruled out, except in scenarios with large warping. A loop-hole to this conclusion arises in the axiverse, where an axion string could be composed of multiple different axion mass eigenstates; a heavier eigenstate could collapse the network earlier, allowing for the QCD axion to produce the correct DM abundance and also generating observable gravitational wave signals.

The quantum kinetic equation for the gauge-invariant Wigner function, constructed from spinor fields that obey the Dirac equation modified by $CPT$ and Lorentz symmetry-violating terms, is presented. The equations for the components of the Wigner function in the Clifford algebra basis are accomplished. Focusing on the massless case, an extended semiclassical chiral kinetic theory in the presence of external electromagnetic fields is developed. We calculate the chiral currents and establish the anomalous magnetic and separation effects in a Lorentz-violating background. The chiral anomaly within the context of extended quantum electrodynamics is elucidated. Finally, we derive the semiclassical Lorentz-violating extended chiral transport equation.

One of the celebrated tools in explaining the hydrogen atom is Born-Oppenheimer approximation. The resemblance of $QQ\overline{q}\overline{q}$ tetraquarks to hydrogen atom within quantum chromodynamics implies usage of Born-Oppenheimer approximation for these multiquark states. In this work, we use dynamical diquark model to calculate mass spectra and sizes of doubly charmed and charged tetraquark states denoted as $T_{cc}^{++}$. Our results for mass spectra indicate some bound-state candidates with respect to corresponding two-meson thresholds. Calculation of expectation values of $\sqrt{⟨r^2⟩}$ reflects that doubly charmed and charged tetraquark states are compact.

In the framework of the Nambu–Jona-Lasinio model beyond mean field approximation, the effects of pion fluctuations on (inverse) magnetic catalysis and magnetic susceptibility are studied. The negative magnetic susceptibility at low temperature is observed when contributions from both neutral and charged pions are taken into account. In the weak field approximation, it is observed that at finite temperature, the magnetic inhibition effect in the chiral limit, resulting from the difference between the transverse and longitudinal velocities of neutral pions, converts to weak magnetic catalysis when considering a nonzero current quark mass. Moreover, the magnetic catalysis is amplified by the charged pions. Therefore, no inverse magnetic catalysis is observed when considering pion fluctuations.